Well I know you guys have seen the treadmill Skyrim setup right? You could only play as long as you could walk, so that in itself is a pretty good limit. In my opinion that will be a really good time limit and will get people some exercise. I hope every game incorporates that setup eventually, and imagine if there were like haptic plates surrounding you, you could reach out and feel the world. And artificial smells are possible too now. If one wanted to, in the near future, you could experience an entirely new world with every sense.
